Amyotrophic lateral sclerosis (ALS), a motor neuron disorder that affects approximately 30,000 individuals in the U.S. alone, is characterized by relatively rapid degeneration of upper and lower motor neurons, with death normally occurring 2-5 years following diagnosis due to respiratory paralysis. Transplantation of neural precursor cells (NPCs) is a promising therapeutic strategy for treatment of traumatic CNS injury and neurodegeneration, including ALS, because of the ability to replace lost or dysfunctional CNS cell types, provide neuroprotection, and deliver gene factors of interest. Previous NPC transplantation studies in ALS therapy have focused mostly on motor neuron replacement;however, this is a challenging strategy because of problems associated with motor neuron differentiation and establishment of connections with host neurons and musculature. Studies in ALS models have suggested that cellular abnormalities are not limited to motor neurons. Given these observations, this proposal aims to target the replacement of non-neuronal cell types for possible therapeutic benefits. Specifically, the therapeutic potential of Glial-Restricted Precursors (GRPs) - lineage-restricted NPCs whose differentiation is restricted to astrocytes and oligodendrocytes - will be assessed following transplantation into the spinal cord of SOD1G93A rats, a rodent model of ALS. Wild-type GRPs or GRPs engineered to over-express the astroglial glutamate transporter, GL1T1, will be transplanted into the ventral horn of the cervical spinal cord of SOD1G93A rats. In Aim #1, fate of transplanted cells will be examined, including survival, migration, differentiation, and glutamate uptake. In Aim #2, transplant recipient animals will be assessed for a number of phenotypic and pathohistologic measures to determine therapeutic efficacy of transplanted cells. In Aim #3, the ability of transplanted GRPs to specifically rescue diaphragm function will be tested. Lay summary: Amyotrophic lateral sclerosis (ALS or Lou Gehrig's Disease) is a devastating nervous system disorder that results in paralysis and ultimately death due to respiratory failure. Transplantation of stem cells derived from the central nervous system is a promising therapeutic strategy for treatment of brain and spinal cord disorders such as ALS because of their unique ability to replace lost or dysfunctional cell types. The work proposed in this study is of great therapeutic relevance to public health because it aims to utilize transplantation of stem cells to replace dysfunctional cells types that contribute to disease progression in ALS, potentially slowing or halting disease.